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Articles by J. Alex Knoll

The Geminid meteors are unique

This week’s celestial highlight is the annual Geminid meteor shower, which peaks late Saturday and before sunrise Sunday. This coincides with the rising waning moon, which just shy of last-quarter still shines quite bright. Fortunately, the Geminids are some of the brightest “shooting stars,” and given patience and a dark spot away from urban glare, you could still expect to see one or two meteors each minute. Plus the Geminids generate a fair number of meteors for several days before and after the peak.
    Like all meteor showers, the Geminids occur as earth passes through a trail/stream of cosmic dust and detritus. As these bits of rock and ice hit our atmosphere, they burst into flames. While the end results are the same, the source of the Geminids’ debris trail is unique. In every other case, these trails of debris are left by comets orbiting the earth in the same way as the planets. The source of the Geminids, however, is a five-kilometer asteroid, known as 3200 Phaethon, that passes between the sun and Mercury every 1.4 years.
    And where comets orbit the sun with a long tail releasing a trail of flotsam, 3200 Phaethon has no tail but somehow produces a trail of debris anywhere from five to 500 times larger than any spawned of comets. Instead of a tail of its own releasing fragments as it’s heated by the sun, 3200 Phaethon pulls bits of dust and debris into its wake as it travels the solar system in a way astronomers are still trying to explain.
    Many meteor showers have been seen since the dawn of civilization, but not the Geminids. They were first noted in 1862 — simultaneously — by an American and a British astronomer, who each recorded an average of 14 meteors an hour. Year by year, that number grew, even as astronomers searched for the shower’s source. Then in 1983, armed with the Infrared Astronomical Satellite, they found 3200 Phaethon to be the parent of the Geminids. By that time, the shower had grown to an average of 120 meteors an hour under good conditions!
    With clear skies you can see the spawn of 3200 Phaethon anywhere in the dark sky, but all point back to the constellation Gemini.
    While you’re at it, look for Jupiter rising in the east-northeast around 10pm and high in the south come dawn. Saturn rises just ahead of the sun in the east-southeast. And Venus and Mars are both visible after sunset.

When there aren’t 24 hours in a day

The full moon rises at sunset Friday and sets at daybreak Saturday morning. Look for it less than about two degrees from Aldebaran, the heart of Taurus the bull. December’s full moon is known as the Cold Moon, the Long Night Moon and the Moon Before Yule. And as we approach winter solstice, these are the longest nights of the year.
    In fact, Sunday marks a turning point in the tug between light and dark, with the earliest sunset of the year at 4:45. Why, you may ask, is the earliest sunset separated from the shortest day of the year by two weeks? Two factors come into play, one celestial the other of our own contrivance.
    Earth’s elliptical orbit around the sun creates a skew in the exact point of solstice — the overall shortest day — and the earliest sunset and the latest sunrise, which won’t occur until January 4 for us along Chesapeake Bay.
    Additionally, modern timekeeping bases each day on a 24-hour cycle. However, the time between one sunrise and the next — or one sunset and the next or high noon from day to day — seldom adds up to an even 24 hours. The cycle of a solar day is dictated by the time it takes for the earth to make one full rotation. And the speed of earth’s rotation changes, spinning faster when closer to the sun, as it is this time of year, and spinning slightly slower when it is farther away in June, July and August.
    So while the time of sunset will hold for the next week or so, we will continue to lose another six minutes of sunlight in the early mornings before reaching solstice December 21 and more still until January 4.
    Venus is slowly pulling away from the sun, appearing for a few minutes in our early evening sky before disappearing below the southwest horizon. At week’s end this evening star sets roughly 40 minutes after the sun, but each night she appears a little higher and remains visible more than a minute longer than the night before. Even so, you may need to scour the horizon with binoculars to see this planet so early in its evening apparition.
    Mars, too, comes into view as the sun sets, quite a bit higher than Venus but also dimmer. Shining at first-magnitude, the red planet is as bright as the average star — enough to be seen during full moon. While pulling away from earth, it nonetheless maintains its brightness through December and remains in view until setting around 8pm.
    Around 10pm, Jupiter rises in the east-northeast, the brightest object at that time other than the moon. By dawn it is high in the south, with the much fainter blue-white star Regulus 10 degrees to its lower left. The night of the 10th, Jupiter trails the waning gibbous moon by about the same distance. The two travel together throughout the dark hours, shining high in the southwest as dawn approaches.
    If you’re up in the hour before dawn, you may be able to spot the return of Saturn. It is quite low in the east-southeast as the sky begins to lighten, another target perhaps requiring binoculars to see amid the growing glare. But each morning it creeps a little higher and by month’s end is visible a full hour before sunrise.

Constellation joins moon and Jupiter, hosts meteors

As twilight gives way to darkness, look for Mars low in the south-southwest. At first magnitude, the red planet is no brighter than your average star, so scouring the horizon with binoculars may help you find it. Can you make out the teapot shape of Sagittarius below? Mars is just above the handle, while the spout points toward the now-set sun.
    Jupiter rises in the east-southeast a little before midnight, and by 6am it is almost directly overhead. Early Friday morning it is less than 10 degrees above the last-quarter moon. Saturday the moon is just below Aldebaran, the heart of Leo the lion. Sunday Jupiter, Regulus and the moon form a near-straight line, each roughly 10 degrees apart.
    The following nights, the moon shifts eastward compared to Jupiter and Regulus, until Wednesday a thin crescent rises before dawn with blue-white Spica just three degrees away.
    The waning moon shouldn’t interfere with the peak of this year’s Leonid meteor shower in the wee hours Tuesday morning. With clear, dark skies you may see 15 to 20 meteors in a given hour. The meteors can appear anywhere in the sky, but traced back they appear to emanate from the shower’s namesake, Leo.

The lonely star swims with the fishes

Thursday’s full moon is known as the Beaver Moon or the Frosty Moon. It rises around sunset and sets around sunrise. Friday and Saturday the moon is with Taurus, the bull’s red eye Aldebaran high to the left and the Pleiades star cluster higher still. Monday night look for the moon near the Gemini twins Castor and Pollux.
    Mercury is at the tail end of its best pre-dawn appearance of the year. The innermost planet rises in the east-southeast around 5:30 at week’s end and is 10 degrees above the horizon as daybreak approaches. Mercury outshines any nearby stars, but that doesn’t make it easier to spot, but binoculars will help you find it tight against the horizon. Don’t confuse it with Spica a bit higher and to the right or with golden Arcturus much higher and to the left.
    You shouldn’t have any trouble spotting Jupiter before dawn. The gaseous giant rises before midnight and is almost directly overhead before sunrise. The bright star to its lower left is Regulus, the heart of Leo the lion. With Venus hidden behind the sun, only the moon outshines Jupiter in our night skies. You can compare the two between sunset Wednesday and sunrise Thursday the 13th, when the waning gibbous moon is within 10 degrees of Jupiter.
    The only other planet visible is Mars low in the southwest as evening twilight gives way to darkness.
    Early November marks the peak of two meteor showers, the South Taurids November 5-6 and the North Taurids November 11-12. Neither is a prolific shower, and both suffer the moon’s bright glare. But they both have staying power, producing a meteor here, a meteor there for days. Better yet, every now and then these slow movers burst aflame, crossing the sky as fireballs.
    Glance to the south after sunset this time of year and you’re not likely to see much except one bright, blue-white star known as the Lonely One. Fomalhaut appears all the brighter due to the company it keeps. Part of Pisces Austrinus, the Southern Fish, Fomalhaut is the only first-magnitude star amid autumn’s dim, ethereal, water constellations. Only after your eyes have had a chance to adapt to the darkness will you see the creatures within this celestial aquarium: Pisces the fish, Cetus the whale, Aquarius the water carrier, Capricornus the sea goat and Delphinus the dolphin.

Halloween falls right in between

The waxing moon reaches first-quarter Thursday, and as darkness falls on Halloween, it shines high in the south, with the bright star Fomalhaut almost straight below.
    As a holiday, Halloween stretches back thousands of years, but not as a day of costumes and trick-or-treating. It coincides with earth’s path around the sun, falling midway between autumnal equinox and winter solstice.
    The Celts of pre-Christan Britain called this cross-quarter day Samhain, celebrating both the end of the harvest and the end of the year. On this night, the veil between the world of the living and the realm of the dead was thought to be especially thin, so people lit bonfires and lanterns from hollowed-out gourds to ward off spirits.
    As Christianity spread, it merged its own holy days with the pagans’ cross-quarter holidays. Imbolc became Candlemas, now better known as Groundhog Day; Beltane gave way to May Day; Lugnasad became Lammas. And Samhain was absorbed into All Saints Day or Hallowmas, marked on November 1, with the night before Hallow’s Eve.
    Now the cross-quarter day coincides with another ritual, setting our clocks back an hour in the return to Standard Time at 2am the first Sunday of November.
    The first week of November provides the best view of Mercury before dawn. The innermost planet reaches greatest elongation November 1, its farthest west of the sun and its highest in our sky. An hour before sunrise, look for it not quite 10 degrees above the east-southeast horizon — roughly the size of your fist at arm’s length. At magnitude –0.6, Mercury is brighter than any nearby star (all but Sirius, in fact), but binoculars may help locate it in the glow of twilight. Don’t confuse the bright planet for Arcturus higher in the east-northeast.
    You shouldn’t have any trouble finding Jupiter. The gaseous giant rises around midnight, and as dawn approaches it is high in the southeast, bluish Regulus and the other stars of Leo the lion stretched out below it.
    Mars is the only planet visible in the evening, shining no brighter than your average star but still a distinct orange-red. Look for it low in the southwest as darkness settles, where it will remain the rest of the year.
    Early November marks the peak of the South Taurid meteor shower. The higher the constellation Taurus, the more meteors you’re likely to see, although the waxing moon will limit you. Still, the Taurids can deliver the occasional fireball.

Even eclipsed, this star blinds

If you didn’t already know about the partial solar eclipse just before sunset Thursday, you’re not likely to have solar glasses at the ready. Do not look at the eclipsed sun for even a moment as it can cause lasting eye damage or blindness. But you can still watch safely with little preparation.
    Try projecting the image through binoculars. Cover one lens and aim the other at the sun, pointing the eyepiece toward the floor or a piece of paper until the sun’s orb appears. Bring it into focus, and voila! You may want to use a tripod, and you can use a small telescope in the same fashion.
    Another option for watching the sun is a pinhole projector, a perennial science project requiring only two sheets of white paper and a pin. Poke a clean round hole in a sheet of paper. With your back to the sun, hold the pierced paper between the sun and the second sheet of paper until you see the sun’s inverted image projected onto it. Increasing the distance between the two sheets enlarges the image but decreases its sharpness. Or you can get more elaborate using the same principles with a box large enough to put over your head to create a viewing chamber.
    Here along Chesapeake Bay, the eclipse begins Thursday at 5pm with the sun low in the west. Alas, it will still be in full swing come sunset at 6:17pm.
    The eclipse won’t be your only chance to put a pinhole projector to use. The sun right now is in the midst of a massive solar storm, resulting in sunspots large enough to see with the protected-but-unaided eye.
    Sunspots start as massive magnetic bursts deep within the sun that migrate to its surface. While highly charged, this energy is cooler than the sun itself, thus appearing darker than surrounding areas. Once to the surface, the energy flares into space in what are called Coronal Mass Ejections, which can wreak havoc on satellites and take down sections of the power grid. Already the International Space Station has turned to face away from the sun to limit the damage from this solar storm.
    Out of all this violence comes beauty, too, in the form of the Northern Lights. So keep a lookout, as a solar storm of this magnitude could make them visible this far south. Learn more at SpaceWeather.com.
    The moon returns to view Saturday as a thin crescent very low in the west-southwest. Look to its lower right for Saturn. As the moon waxes into the new week, it shines near the planet Mars.

It’s a crowded solar system

If you’ve been out before dawn you’ve likely seen Jupiter blazing in the east. Early Friday morning, the gaseous giant shines left of the waning crescent moon. The following morning you’ll find it above the moon and forming a loose triangle with the star Regulus, the heart of Leo the lion.
    The only other naked-eye planets visible are Mars and Saturn, low in the western sky in the darkening twilight. Saturn is fast on the heels of the setting sun, while Mars is farther to the east. Don’t confuse Mars for Antares, the red heart of Scorpius and roughly midway between the two planets.
    Mars has a close encounter Sunday, when Comet Siding Spring (C/2013 A1) passes within 82,000 miles of the red planet. For comparison, the moon orbits the earth by almost 240,000 miles, and the closest recorded comet to pass us was in 1770 at 1.4 million miles! While a collision isn’t predicted, the comet’s tail will likely engulf the red planet. Even with binoculars you’ll be hard-pressed to see Comet Siding Spring, but a telescope will reveal it above the red planet.
    We have our own close encounter with a comet — Halley’s Comet, no less — in the form of the annual Orionid meteor shower, which peaks late Tuesday and early Wednesday. The comet hasn’t visited the inner solar system since 1986, but each year at this time earth passes through the trail of debris left behind from its countless orbits around the sun. With the waning crescent moon rising shortly before dawn, you might see from 20 to 25 meteors an hour. They can appear anywhere in the sky, but if you trace back their path they radiate from the constellation Orion.
    The sun and moon have a close encounter of sorts Thursday the 23rd, resulting in a partial solar eclipse in the early evening. Be warned: Gazing upon a solar eclipse can cause blindness, and a partial eclipse is all the more dangerous, so look only with a solar filter.
    Just as it takes a full moon for a lunar eclipse like the one two weeks ago, a solar eclipse coincides with new moon, when it passes between sun and earth, blotting out the sun’s disc — or part of it in the case of this partial eclipse.
    Hereabouts the show begins at 5:52pm, with the greatest point of eclipse coming at 6:08, when one-third of the sun is blocked from view. Alas, the sun sets at 6:17 before the eclipse is over.
    Again, do not attempt to watch the eclipse without protective eyewear; use the coming week to find solar glasses or another proper filter.

Its far side is always dark to us

The dark hours at week’s end are still brightened by the glow of the waning Hunter’s Moon, which rises mid-evening and dominates the night sky until daybreak. On clear days this week, you may even see the moon in the west after sunrise.
    Over the weekend, the moon travels with the constellation Taurus. Friday it is 10 degrees to the right of the Pleiades star cluster while the bull’s red eye Aldebaran is a little farther below the moon. The brightests stars of the Pleiades form a small but distinct dipper, which makes up the bull’s back. Saturday the moon is much closer to Aldebaran and the Hyades star cluster, which makes up the bull’s face. If the moonlight is too much to discern these stars, wait a day or two until the waning moon has shifted to the west.
    Just like here on earth, half the moon is always illuminated by the sun and the other half facing away from the sun. But as the angle between the sun, earth and moon changes, so does the portion of the moon’s illuminated face that we can see. With the moon waning, the angle is closing, obscuring more of the lunar surface behind earth’s shadow. This darkened section of the moon still faces earth and should not be confused with the so-called dark side of the moon. Better to think of that as the far side of the moon, which faces away from earth. The far side is still bathed in sunlight — we are just never in a position to witness it.
    The moon rotates on its own axis, with one side facing the sun for about two weeks and then facing away from the sun the next two weeks. Over billions of years, earth’s stronger gravitational pull has slowed the moon’s rotation to the point that it spins in synch with its pace around the earth. As a result, one side of the moon faces earth only during new phase, when it is between us and the sun, obscured by the light of day. So we never see the far side of the moon.
    Mars and Saturn pop into view in the wake of the setting sun. Saturn is sinking fast and is visible for less than an hour. Mars is well to the east of Saturn but not quite as bright. Don’t confuse it for the similarly hued star Antares, the heart of the Scorpion wriggling below.
    Jupiter rises around 2am and is high overhead in the east as morning approaches. Over the next month this gaseous giant climbs higher and grows brighter in our pre-dawn sky.

Earth’s shadow blots out this week’s full moon

With sunrise now after 7am, perhaps you’ve seen an exceptionally bright light in the south before dawn? Looking up, did you see the constellation Orion? That’s Sirius, the brightest star in the heavens, known as the Dog Star for its place amid Canis Major. Sirius rises around 2am in the east-southeast. Close to the horizon, it pulses a dazzling rainbow of colors, its light refracted by earth’s atmosphere like that from a prism. Closer to daybreak, when Sirius is high in the south, its light cuts through less of our atmosphere and appears a brilliant, cold white. As if Sirius didn’t stand out from its brightness alone, the three belt stars of Orion point straight down to the Dog Star.
    Perhaps, though, you’re looking due east in the hour before sunrise. In that case you’re seeing Jupiter, which outshines even Sirius. The giant planet rises around 3am, and by 6am it is high in the east. Below Jupiter is the constellation Leo with its upper body looking like an inversed question mark with Regulus at the bottom.
    You’ll want to get up before dawn Wednesday to catch the total lunar eclipse of the full, Hunter’s Moon. An eclipse of the moon only occurs during full moon, when it is aligned just so with the earth and sun, which casts earth’s shadow over the lunar surface. The process begins after 4am as the moon grows darker under the outer, penumbral, shadow. A little after 5am, the full, umbral, shadow begins to take a growing bite from the moon’s left edge until it is completely over-shadowed by 6:30. Mid-eclipse is at 6:54, after which point the rising sun breaks the spell.
    At the other side of darkness, Mars and Saturn appear at sunset. Saturn is fast on the heels of the sun, low in the southwest at dusk. Night by night the ringed planet is sinking lower and inching closer to the sun until it disappears around month’s end. Mars trails Saturn by roughly 20 degrees. Normally its red hue makes it easy to spot, but you may think you’re seeing double, as Mars is less than five degrees above another red light, Antares, the heart of Scorpius, whose name means rival of Mars. Over the coming weeks Mars creeps higher while the scorpion sets from view for winter.

The equinox ushers in fall

Week’s end finds the waning crescent moon in the company of Jupiter before dawn. Around 6am Friday morning, look for the moon high in the east with Jupiter to its lower left. The same time Saturday the moon shines just six degrees from Old Jove. Then Sunday, the now razor-thin crescent is well below Jupiter, while the first-magnitude star  Regulus, is just six degrees away.
    While you should have no trouble spotting the waning crescent moon and Jupiter in the east before dawn, Venus is a trickier target. This Morning Star rises less than an hour before the sun, and that window of visibility shrinks by about a minute each day.  At best Venus is only 10 degrees above the horizon before sunrise, so you may need to scour the eastern skyline with binoculars to pinpoint Venus’ otherwise dazzling glow.
    This time of year before dawn offers the best chance to spot the eerie zodiacal light also called false dawn. You need dark skies away from any urban glare to see the zodiacal light, which glows like milky pyramid of light rising from the horizon an hour or two before actual dawn.
    Unlike true dawn, the zodiacal light is a pale, ghostly glow devoid of the rosy tint from the coming sun, which is caused by light entering earth’s atmosphere. The zodiacal light is actually sunlight reflecting off countless bits of dust and detritus within our solar system that orbit the sun along the same path as the planets. This time of year the ecliptic — the path of the sun, moon and planets — stands nearly straight up with respect to the eastern horizon before dawn.
    At the other end of darkness, Mars and Saturn shine low in the southwest in the early evening. Of the two, Saturn is slightly brighter and is farther west, setting around 9:30pm. Mars isn’t far behind, setting shortly after 10. But while the ringed planet is weeks away from disappearing amid the glare of the sun, Mars remains a fixture in our early evening skies for weeks to come.
    A clear view to the west-southwest immediately following sunset may reveal Mercury burried in the horizon. Binoculars will help, but don’t confuse it with nearby Spica, which is only a couple degrees away through the weekend. They are so close that both will appear in the same field of view using binoculars or a telescope.
    Monday at 10:29pm EDT, the sun is poised directly above the equator somewhere in the vicinity of New Guinea. On that day or the following, the sun rises due east and sets due west, dividing the day between near-equal amounts of daylight and darkness for everyone around the globe. For the 90 percent of us living in the Northern Hemisphere, this equinox marks the beginning of autumn.
    Because of the earth’s 231⁄2-degree tilted axis, the Northern and Southern Hemispheres each receive more direct sunlight and warmth than the other for half the year. Twice a year, earth’s tilted axis and its orbit around the sun come together just so that the amount of light and dark are equal around the globe. Hereafter our time in the sun will grow shorter each day as the sun creeps ever southward of due east until reaching winter solstice in late December, its farthest point south in our skies.